Abstract Heterogeneous isotope exchange rates of Na+, Ca+, Ba2+ and Sr2+ in mono-and biionic resin exchangers (Merck I) have been measured under conditions where diffusion is rate determining. For the self-diffusion of Na+, Ba2+ and Sr2+ linear Dt/r2 - f(t)-curves are obtained. Cs-isotope exchange shows non-ideal diffusion kinetics. In mixed Ba-exchangers the self-diffusion coefficients of Ba2+ and Sr2 depend on the ionic composition of the exchanger phase. Ion exchange rates have been measured for Ba/Sr2+ -exchange and its reversal. Computed curves are presented using Helfferich’s theory of ion exchange and an extended treatment with activity correction terms and concentration dependent self-diffusion coefficients. Computed and experimental curves are discussed.